CO₂ Induced Foaming Behavior of Polystyrene near the Glass Transition

Abstract

This paper examines the effect of high-pressure carbon dioxide on the foaming process in polystyrene near the glass transition temperature and the foaming was studied using cylindrical high-pressure view cell with two optical windows. This technique has potential applications in the shape foaming of polymers at lower temperatures, dye impregnation, and the foaming of polystyrene. Three sets of experiments were carried out at operating temperatures of 50, 70, and 100°C, each over a range of pressures from 24 to 120 bar. Foaming was not observed when the polymer was initially at conditions below Tg but was observed above Tg. The nucleation appeared to occur randomly leading to subsequent bubble growth from these sites, with maximum radius of 0.02–0.83 mm. Three models were applied on the foaming experimental data. Variable diffusivity and viscosity model (Model C) was applied to assess the experimental data with the WLF equation. The model shows very good agreement by using realistic parameter values. The expansion occurs by diffusion of a dissolved gas from the supersaturated polymer envelope into the bubble.

Assessing the Impact and Suitability of Dense Carbon Dioxide as a Green Solvent for the Treatment of PMMA of Historical Value

“…Carbon dioxide impregnates the polymer matrix to a different degree, depending on various factors, such as experimental conditions and polymer type [ 74 ]. Upon depressurization, CO 2 that has already dissolved in the polymer matrix can become supersaturated and nucleate bubbles, which induces foam or minor defects in the polymer structure [ 105 , 106 , 107 , 108 ]. Induced bubble formation, growth, and foaming are methods widely used in polymer processing for various applications, such as creating a porous structure into polymers, and for drug loading [ 32 , 73 , 74 , 109 , 110 ].…”